As known, a lens module that is driven by a voice coil motor (VCM) is advantageous for reducing the overall size of the lens module and lowering the product price. Nowadays, the voice coil motor is applied to the lens module having an auto focus function and/or an auto macro function. The auto focus function enables the optical system to obtain correct focus on a subject without requiring the operator to manually adjust focus. The auto macro function allows for close-up shots when the distant from the subject is very short. As known, the method and the device currently used to control the auto macro function of a VCM-driven lens module are very complicated and costly.
FIG. 1 is a schematic circuit block diagram illustrating a device for controlling an auto focus function of a lens module according to the prior art. As shown in FIG. 1, the lens module 11 has a coil 111. The coil 111 has a first terminal A1 and a second terminal B1. The controlling device 10 principally comprises a multi-stage controlling module 12 and a micro processor 13. The multi-stage controlling module 12 and the lens module 11 are connected to each other in series. The micro processor 13 and the multi-stage controlling module 12 are connected to each other in series. The first terminal A1 is electrically connected to a power source Vcc. The second terminal B1 is electrically connected to the multi-stage controlling module 12.
Hereinafter, the operations of the controlling device 10 will be illustrated with reference to FIG. 1 First of all, a control signal S11 is issued from the micro processor 13 to the multi-stage controlling module 12 according to a desired focal length. In response to the control signal S11, the power source Vcc issues a current S12 to the multi-stage controlling module 12. The current S12 is a variable current with various electric levels, and a specified electric level of the variable current S11 is selected according to the desired focal length. The lens module 11 has a magnetic yoke (not shown) and several magnets (not shown), wherein the magnets are attached on the magnetic yoke to provide a permanent magnet field. The magnets axially surround the coil 111 and are separated from the coil 111 by a gap. When the variable current S12 passes through the coil 111, a magnetic force will be generated on the coil 45 while applying moving the lens holder that carries an optical lens (not shown). As such, the optical length of the lens is shifted by a specific distance so as to obtain correct focus on a subject.
In other words, the conventional controlling device 10 and the conventional controlling method as described in FIG. 1 are mainly applied to control the auto focus function of the lens module 11. In response to the control signal S11, the electric levels of the variable current S12 are adjusted according to the desired focal length. Since the electric levels of the variable current S12 are adjustable, the lens of the lens module can be moved to a specified distance when a proper magnitude of the variable current S12 passes through the coil 111. Generally, the multi-stage controlling module 12 is implemented by a driver IC because the process of performing the auto focus function is very complicated.
For implementing an auto macro function on the basis of the controlling device 10, many manufacturers may alter some operating modes of the driver IC of the multi-stage controlling module 12. For example, except that the maximum focal length mode and the minimum focal length mode are enabled, the other focal length modes of the driver IC are disabled. Alternatively, the driver IC may change the flowing direction of the variable current S12 to move forward or backward the lens of the lens module 11 in order to implement the auto macro function.
Since the use of the driver IC to implement the auto macro function of the lens module is very costly, there is a need of providing a cost-effective device for controlling the auto macro function of the lens module.